I got really interested in physics in 6th grade, and relativity in 7th grade,
after my dad called me down to watch the following on PBS tv:
Einstein's Universe ( see below for the video, which is now available online by the film distributor ).
My uncle then gave me a book, which was a "gift" given to him for being a supporter of public television:
the accompanying book by Nigel Calder (
https://www.amazon.com/dp/0517385708/?tag=pfamazon01-20 )!
I ate that book up... and was thirsty for more.
I went through various pop-science books...
which offered what seemed like wild, but interesting ideas, but no details.
I then realized that for me to really get anywhere,
I had to read textbooks.
So,
even if I wasn't ready to read and study the textbooks as if I were taking a course at the time,
I read what I could to get a glimpse of what the big ideas are
and a glimpse of the details I would need to someday understand those big ideas.
I got The Feynman Lectures on Physics and tried my best to read and re-read various passages.
It was low-pressure, occasional reading.
In high-school and in college,
in addition to the textbook for the course,
I would occasionally get the textbook for the next course,
again to get a glimpse of what lies ahead.
So, I stand by my comments [here and earlier] about the Feynman Lectures for the OP, an 8th-grader.
And these days, there are a lot of resources available online
e.g.
https://www.feynmanlectures.caltech.edu/
and
https://www.google.com/search?q=youtube+feynman+lectures
and now,...
Here is
Einstein's Universe (1979)... staring Peter Ustinov, Nigel Calder,
with appearances by Sidney Drell, Roger Penrose, Dennis Sciama, Irwin Shapiro, John Archibald Wheeler, and others
https://www.imdb.com/title/tt6061610/